Multilayered electrostatic transducer

1 . An electrostatic transducer comprising:

first and second flexible conductive membranes; and

first and second conductive stators;

wherein the first and second flexible conductive membranes and the first and second conductive stators are assembled in a layered configuration with the membranes between the stators and with enclosed volumes of air between the first and second membranes;

wherein the enclosed volumes of air do not permit air to move freely in or out of the volumes in a way that transmits an acoustic wave;

wherein the first and second membranes are mounted in the transducer with a spacer between them, wherein the first and second membranes together with the spacer enclose the volumes of air;

wherein the spacer comprises a layer of material with apertures separated by walls and each aperture defines a respective one of the volumes of air that is sealed in by the membranes;

wherein the spacer is bonded to the first and second membranes to seal the air inside the enclosed volumes;

wherein the spacer has a hexagonal lattice shape; and

wherein the electrostatic transducer is configured to apply an electrical potential which gives rise to an electrostatic force between the membranes and the stators that causes the membranes to move relative to the stators.

2 . The electrostatic transducer as claimed in claim 1 , wherein a spacing between the first and second membranes is at least 5 μm.

3 . The electrostatic transducer as claimed in claim 1 , wherein the first and second membranes are electrically coupled.

4 . The electrostatic transducer as claimed in claim 1 , wherein the transducer further comprises one or more further membranes between the first and second stators.

5 . The electrostatic transducer as claimed in claim 1 , wherein at least one of the first stator, the second stator and a further stator comprises an insulating coating on one or more surfaces facing the membranes.

6 . The electrostatic transducer as claimed in claim 1 , wherein the first and second flexible conductive membranes have respective first and second effective compliances, wherein the first effective compliance is at least 10% greater than the second effective compliance.

7 . A method of manufacturing an electrostatic transducer, the method comprising:

providing first and second flexible conductive membranes and first and second conductive stators;

assembling the first and second flexible conductive membranes and the first and second conductive stators in a layered configuration with the membranes between the stators and with enclosed volumes of air between the first and second membranes; and

arranging the electrostatic transducer such that the electrostatic transducer is configured to apply an electrical potential which gives rise to an electrostatic force between the membranes and the stators that causes the membranes to move relative to the stators,

wherein the enclosed volumes of air do not permit air to move freely in or out of the volumes in a way that transmits an acoustic wave;

wherein the first and second membranes are mounted in the transducer with a spacer between them, wherein the first and second membranes together with the spacer enclose the volumes of air;

wherein the spacer comprises a layer of material with apertures separated by walls and each aperture defines a respective one of the volumes of air that is sealed in by the membranes;

wherein the spacer is bonded to the first and second membranes to seal the air inside the enclosed volumes;

wherein the spacer has a hexagonal lattice shape.

8 . A method of manufacturing the electrostatic transducer of claim 1 , the method comprising:

providing the first and second flexible conductive membranes and the first and second conductive stators;

assembling the first and second flexible conductive membranes and the first and second conductive stators in the layered configuration with the membranes between the stators and with the enclosed volume of air sealed between the first and second membranes; and

arranging the electrostatic transducer such that the electrostatic transducer is configured to apply the electrical potential which gives rise to the electrostatic force between the membranes and the stators that causes the membranes to move relative to the stators.